Digital Sensor Technology for Grain Bins

The first direct-to-digital temperature sensor with multiple connections on a single line was introduced by the Dallas Semiconductor Corporation (Maxim Integrated Products) in 1995.

Today's direct descendent is the digital temperature cable option now available for farm grain storage systems.

The Dallas 1-Wire protocol can identify the temperature of a specific sensor and report back to a central processor up to 300 meters away. Each microchip on the wire has a unique serial number.

According to a 1995 Business Wire report, product manager Rick Downs said, "The DS1820 provides nine-bit temperature readings. Only one wire (plus ground) needs to be connected from a central microprocessor to a DS1820 to send information back and forth. A worker can stand at the host station and read temperatures remotely. This solution gets rid of a lot of the analog and circuitry, and it reduces the need for shielded cable."

The device stores energy on an internal capacitor during periods when the signal line is open, and it operates off this power reserve when it is sending a signal.

Going digital
Today, at least two companies use 1-Wire digital cable technology for farm storage systems: NAB Automation and OPI-Integris.

"NAB Automation is the manufacturer of the digital Eagle Eye bin temperature monitoring system," says Marty Scudder, NAB Automation. "Our systems are suitable for small to large farmers, co-ops, and large corporate grain terminals."

Eagle Eye, introduced in 2011, has its operating procedures built into a programmable logic controller (PLC) box. The PLC is mounted inside a master control room; it can't be reprogrammed and it can't get viruses. Other than a lightning strike or power outage, nothing will knock down the program, says Scudder.

When NAB updates the PLC, the new box is shipped to the farm with installation instructions. If that's an issue, NAB engineers will walk you through the installation.

"Our technology is based on the Dallas Semiconductor 1-Wire platform," explains Scudder. "Simply put, the Eagle Eye cables use microchips in place of thermocouples. Multiple chips reside on a single wire, and these chips are polled by our remote-sensing units. All data from multiple sensors residing within the cable is transmitted in one string. Data transmission in this form produces a much faster and more reliable transmission rate than analog thermocouple technology."

Each digital cable requires only one termination or switching point, regardless of the number of microchip sensors on the cable.

Simple service
OPI-Integris adopted the 1-Wire system earlier than Eagle Eye. Scudder says both use a single line inside a cable with sensors at 6-foot spacing. If something goes wrong with a microchip or capacitor, the company will send a replacement line. The line is retractable from the cable.

"It's like unplugging a worn-out extension cord and replacing it with a new one," says Scudder. "That would be the extent of the service on it."

The option for reading humidity in grain storage is an important feature of the OPI-Integris system. NAB has a similar option but sees it as appealing to a small market segment.

"It's not going to tell you the moisture of the grain," says Scudder. "It only tells you the moisture of the air surrounding the grain. If that's 2% off and you deliver the grain to market, that's a big hit to the farm."

There are other differences in servicing and pricing, he says, between the two digital cable suppliers.

An option to add hazard monitoring sensors for gearboxes and bearings in a grain-handling system is also available from the Eagle Eye manufacturer.